The present invention relates to recording and reproducing technique on a digital audio tape by a stationary head, and more particularly to method and apparatus suitable for correcting and concealing a data error such as a dropout in a record medium.
A multi-track, Stationary-head Digital tape recording/reproducing apparatus Audio Tape-recorder (S-DAT) has been well known in the art of digital audio system.
Many audio data recording formats have been proposed to prevent or correct data errors in recording and reproducing the data. As an example, an interleaved format is shown in an article entitled "Stationary Head Digital Audio Tape Deck" by Uchida et al, Technical Report of Institute of Electronics and Electrical Communication of Japan, Vol. 81, EA 81-64, p. 38 (1981). In the disclosed audio recording/reproducing method, a CIRC (cross-interleaved Reed Solomon code) is used to correct the data error. By nature of a magnetic tape, a burst error which is much longer than a bit length, that is, a data dropout frequently occurs. Accordingly, the data is interleaved to convert the burst error to a random error. FIG. 2 shows an interleaved data in the above system. The interleaved data is arranged in a parity track located at a center of the tape and a data signal track located at an edge are of the tape. Twelve words (1 word=16 bits, one sampling data) of left (L) and right (R) channels sampled from a two-channel stereo signal are represented by 24 symbols (1 symbol=8 bits, error correction unit) to which 4 parity symbols are added to form 28 symbols, which is arranged on the tape. After the interleave, four parity symbols are further added on the tape to form a 32-symbol data. The correction is made in two steps for the widthwise data and the interleaved 28-symbol data. Up to four symbol errors can be corrected by an erasure correction method. In this system, a correction length is approximately 2.1 mm and an interpolation length is approximately 5 mm. However, no consideration was made in this system to a low error rate at the edge of the tape and a long burst error generated in one of the tracks.
An article entitled "On PCM Multi-Channel Tape Recorder using Powerful Code Format" by K. Tanaka et al, presented at the 67th Convention of the Audio Engineering Society (AES), October 31-Nov. 3, 1980 New York, discloses development of a semi-separate code format. Particularly, FIG. 7 thereof shows a format of odd/even sample data interleaved by a skew pattern with respect to a tape transport direction.
An article entitled "A Multitrack Digital Audio Recorder for Consumer Applications by W. J. Van Gestel et al, in J. AES, vol. 30, No. 12, 1982, December pp. 889-895, presented at the 70th Convention of the AES, New York, October 30-Nov. 2, 1981, particularly FIG. 9 and page 892 disclose a record format on a tape in which the distance between data words terminates in each block and parity check words are added in the block longitudinally and widthwise of the tape.
This error correction technique for correcting the random and burst errors is not sufficient to prevent and correct the data dropout in recording and reproducing the two-channel audio signal on the tape.
The technical trend of the S-DAT is described in the article entitled "Activities of DAT Association", ELECTRONICS published by Electronic Industries Association of Japan, vol. 24, No. 10, 1984, pp. 36-42, particularly pp. 40-42.